Allow width auto

This changes the width to default to 'auto'.

This is a breaking change so it is semver major, and you may need to update existing dialogs.

v1.0.0

A big breaking change

1. Upgraded to React 0.14
   • Also upgraded dependencies
   • Using renderIntoSubtree to preserve parent context for React 0.14
2. Removed CSS
   • Moved most CSS to JSS
   • Moved images to SVG